City of Ottawa

Project Update - Combined Sewage Storage Tunnel (CSST) - April 2019

Picture of the Ottawa River, showing Parliament in the background.

Building a healthy and resilient future for the Ottawa River

This $232.3 million construction project is a key part of the Ottawa River Action Plan (ORAP), which is aimed at enhancing the health of the Ottawa River and protecting our water environment for future generations. A healthy water environment provides safe, abundant drinking water; supports agriculture, recreation and tourism; lessens the impact of flood events; and helps sustain fish and wildlife.

Construction Site Map

The map below identifies construction sites for the CSST project within the City of Ottawa, which are described in more detail here.
Map of the CSST alignment and sites. The East-West tunnel runs through the downtown core from LeBreton Flats to New Edinburgh, and the North-South tunnel runs from Chamberlain Avenue to behind the Supreme Court of Canada. Description of sites, indicated by orange dots, are as follows: Site 1: West End Shaft - LeBreton Flats
Site 2: East West Tunnel/North South Tunnel Intersection - Kent and Slater Streets Site 3a: Rideau Canal Interceptor Diversion Chamber - Confederation Park Site 3b: Rideau Canal Regulator – Rideau Canal Site 3cR: Wilbrod and Cumberland Streets Site 4: St. Patrick Shaft - York and Cumberland Streets Site 5: East West Tunnel Outlet and Rideau River Collector Diversion - New Edinburgh Park Site 6: NST Overflow/Kent Street Outfall - Ottawa River Pathway Site 7: Identified with a grey dot, as this site was eliminated during the design phase of the project Site 8: McLeod Street Drop - Kent and McLeod Streets Site 9: Catherine Street Drop - Kent and Catherine Streets Site 10: Chamberlain Shaft - Kent and Chamberlain Streets
The CSST will consist of two inter-connected tunnels over six kilometres in total length, three metres in diameter, located 10 to 31 metres below surface level. The North-South Tunnel (NST) will run below Kent Street, from Chamberlain Avenue to just behind the Supreme Court of Canada, and the East-West Tunnel (EWT) will run through the downtown core, from Stanley Park to LeBreton Flats, generally under Cumberland and Slater Streets.

Construction is underway at several sites.


Construction Activity Progress


North-South Tunnel (NST)

Tunneling of the NST from Kent/Chamberlain Streets to the Ottawa River (Site 10 to Site 6) is complete!
Picture showing a map of Ottawa and an orange line from Kent and Chamberlain north along Kent Street to behind the Supreme Court of Canada showing that the north-south tunnel has been completed.
Progress on the north-south tunnel (NST).

East-West Tunnel (EWT)

Tunneling of the East-West tunnel from Stanley Park to LeBreton Flats (Site 5 to Site 1) is underway, and progressing below the Rideau Canal toward Centretown.
Picture showing a map of Ottawa and an orange line from Stanley Park W to Cumberland, then south along Cumberland before turning west on Waller/ Laurier and stopping at the Rideau Canal showing that the east-west tunnel has been completed to this point.
Progress on the east-west tunnel (EWT).
Picture inside a cylindrical concrete tunnel showing yellow pipe along the top, tracks on the bottom, and a series of small pipes on the right.
View inside a completed portion of the east-west tunnel.

Site 1: West End Shaft – LeBreton Flats

Site 1 is the western end of the East-West Tunnel (EWT) and the tunnel boring machine’s final exit point. Ultimately, Site 1 will house a flow diversion chamber, an access point for operations staff and large equipment, and an odour control facility (OCF).

Site 1 construction activities of interest:
  • Construction of the OCF walls and roof slab are complete.
  • Commenced weather proofing of the exterior walls, backfilling, and mechanical and electrical servicing inside the building.
  • Construction of the chamber base slab at the bottom of the shaft is complete.
  • Chamber formwork continues in the shaft.
Picture of a large concrete building with an orange tarp around the top.
Exterior works at the OCF.

Site 2: East-West Tunnel/North-South Tunnel Intersection – Kent and Slater Streets

Site 2 is where the two tunnels intersect. Preparations for construction of an underground access chamber at this location have begun.

Site 2 construction activities of interest:
  • Completed utility relocations and installation of sidewalk hoarding and overhead protection along Slater Street.
  • Chamber construction preparations continue underground, at the future intersection of the North-South Tunnel.

Picture inside of a underground chamber with a piece of construction equipment and inside of a large concrete pipe in the distance.
Underground preparation at the NST/EWT intersection.

Site 3A: Rideau Canal Interceptor Diversion/Drop – Confederation Park

Construction of a new underground diversion chamber drop structure and odour control facility is underway at Site 3A. Excess flows from the existing Rideau Canal Interceptor will be diverted to the EWT at this location.

Site 3A construction activities of interest:
  • Continued construction of the underground chamber.
  • OCF building interior and exterior works are complete.
  • Preparations underway for landscaping around the OCF.

Picture showing inside of a large rectangular underground shaft showing a series of steel along in the inside perimeter.
View of chamber construction activity within the shaft.

Site 3B: Rideau Canal Regulator – Rideau Canal

Work is necessary on the existing Rideau Canal Regulator in order to ensure operational efficiency of the CSST.

Site 3B construction activities of interest:
  • Underground maintenance and modifications within the existing Rideau Canal Regulator are underway. The CSST contractor has demobilized, but is expected to return for a few days in April to complete work.

Site 3CR: Wilbrod Shaft – Cumberland Street at Wilbrod Street

Construction of an underground access chamber is underway at this location.

Site 3CR construction activities of interest:
  • Site signage and traffic control remain in place.
  • Completed excavation of the shaft and shaft support works.
  • Work to temporarily re-instate the roadway is underway.
Picture showing a construction site with houses in the background.
Demobilization underway prior to temporary reinstatement of roadway on Cumberland Street.

Site 5: East-West Tunnel Outlet and Rideau River Collector Diversion (New Edinburgh)

Construction continues in New Edinburgh's Stanley Park, where the tunnel boring machine started its east-west journey, and at the intersection of Queen Victoria Street and River Lane (to connect to existing overflow sewer infrastructure).

Site 5 construction activities of interest:
  • Tunneling support operations continue on the surface, at 5A (the main site).
  • Construction of the concrete Interceptor Outfall Sewer chamber continues.
  • Commenced installation of a concrete pipe diversion sewer between the main shaft and shaft 5C (the intersection of Queen Victoria and River Lane).
  • Concrete and steel work underway for chamber construction within the shaft at 5C.
Picture showing a large pipe across the bottom of a large concrete cylindrical shaft with steel being built up around it.
Chamber construction works within the 5C shaft.

Site 6: North-South Tunnel Overflow/Kent Street Outfall - Ottawa River Pathway

Site 6 was the exit point for the tunnel boring machine and the northern end of the North-South Tunnel. Potential overflows from the Kent Street Sewer will be diverted to the NST and monitored here. An underground connection and an improved sewer outfall will also be constructed at this location.

Site 6 construction activities of interest:
  • Work continues within the NST/EWT intersection, with access through the main portal at Site 6.
  • Final works on the NST overflow chamber continue.

Site 8: McLeod Street Drop – McLeod Street and Kent Street

Work on McLeod Street, near Kent Street, is underway to complete the McLeod relief sewer, and construct underground chambers to convey flows to the NST.

Site 8 construction activities of interest:
  • Excavation of both shafts are complete.
  • Rock breaking at the bottom of the 24-metre-deep shaft, to connect horizontally to the new tunnel below Kent Street is underway.

Picture looking down into a rectangular wood shaft which has a smaller cylindrical shaft in its centre.
View towards bottom of the shafts.

Site 9: Catherine Street Drop – Catherine Street at Kent Street

Work at the corner of Catherine and Kent Street, will include construction of two underground chambers to convey flows from the existing sewer on Catherine Street to the new CSST. An odour control facility will also be constructed at this location.

Site 9 construction activities of interest:
  • Continuing underground chamber construction preparation preparation (in the North-South Tunnel).
  • Preparation for construction of the second shaft and the OCF is underway.
A picture looking at a cylindrical tunnel in the middle of two tall wooden walls.
Chamber construction preparations from within the NST.

Site 10: Chamberlain Shaft (Kent/Chamberlain Streets)

Site 10 was the launch shaft for the north-south tunneling operation and, ultimately this shaft will house a chamber which will allow operations staff and equipment to access the tunnel.

Site 10 construction activities of interest:
  • Work continues within the North-South Tunnel, with access through the main shaft at Site 10.
  • Preparatory works in advance of chamber construction at Site 10A.
Picture of a large cylindrical underground shaft showing construction equipment moving dirt at the bottom and wood formwork along the inside walls.
Maintenance at the bottom of EWT access shaft 10a.

Mobility & You

Stay informed about capital infrastructure projects. Check out the City’s interactive traffic map and traffic report or call 3-1-1 for updates about when and where construction is happening.

Contact Us

The CSST Project Team is committed to sharing information that may help affected residents and businesses plan around construction in their neighbourhoods.

For more information:
The CSST dedicated phone number is 613-580-2424 ext 2CSST (22778).
(This does not replace 3-1-1).

Visit us on the web at or email the project team at

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